Elimination of objectionable odors from soap



Patented Nov. 24, 1953 ELIMINATION OF OBJECTIONABLE ODORS FROM SOAP Frederick J. Squire, Milton, and Peter D. Stengel, Belmont, Mass., assignors to Lever Brothers Company, New York, N. Y., a corporation of Maine No Drawing. Application October 7, 1950,

Serial No. 189,054

4 Claims.

This invention relates to a process of preparing soap compositions which are substantially free of objectionable odors, and more particularly to a process of improving hydrosulfite treated soaps to eliminate objectionable odors therein.

Dark-colored fats and oils which are used for the preparation of soaps are frequently bleached prior to saponifieation. Also, some unhardened or poorly processed oils darken in the finished soap or during saponification. To overcome this, bleach may be added.

Sodium and like hydrosulfites have been used for these purposes and may be added in amounts approximately equal to 0.1 to 0.2% at any stage of soap manufacture. However, after addition of the hydrosulfite the soap tends to change in color from cream to a greyish white, and may develop a strong objectionable odor. This odor is difficult to remove by washing and if it persists to the finished cake it may mask the perfume. Various methods have been tried to prevent formation of the odor or to eliminate it, but without success. Apparently it is due to sulfur compounds formed as a consequence of decomposition of the hydrosulfite used.

It has now been determined that addition of a water-soluble zinc compound to the soap before or after treating with hydrosulfite effectively destroys the odor, and at the same time prevents the development of a grey color. The zinc compound is most effective in the presence of water, and is therefore, for example, added to the soap boil after bleaching or at any time up to and including the finish change. In some cases it may be added at the time perfume or other ingredients are added.

Since the origin of the odor is unknown, the action of zinc compounds in overcoming the odor is not fully understood, but because of the change in color of the mass as well as the elimination of odor, it is considered that chemical reaction of some sort occurs between zinc ion and the odor-imparting components of the soap, resulting in formation of a zinc compound which itself is substantially odorless, and white or colorless.

Possibly the odor is due to hydrogen sulfide, which is removed through formation of insoluble zinc sulfide.

The zinc compound may be added to the soap at any stage of manufacture by any of the conventional processes, whether continuous or batch (kettle) methods, such as the full-boiled or settled process, for the preparation of hard soaps,

using sodium hydroxide, and soft potash soaps, in which the glycerine remains in the soap, the semi-boiled process, in which the exact amount of alkali required is employed, and glycerine is retained in the soap, the cold-made process, in which the mass is saponified at a low temperature with slightly less than the calculated amount of lye, the carbonate saponification method, which utilizes fatty acids and alakline carbonates, and the jet saponification method.

In the full-boiled process the zinc compound may be added to the kettle during any of the changes, such as the initial saponification, or the strong change, the weak change or the finish change.

Any organic or inorganic zinc salt or other compound of zinc which is soluble in water to an appreciable extent is effective for this purpose. In the commercial application of the invention, it is preferred to employ inexpensive zinc salts, such as zinc chloride or zinc sulfate, but the acetate, borate, bromide, bromate, carbonate, chromate, nitrate and thiocyanate may also be used.

The zinc compound may be combined with the soap in solid form or in aqueous solution and at elevated or room temperatures. Reaction is complete within a few seconds or minutes after mixing.

The process is applicable to water-soluble ammonium, sodium and potassium soaps of fatty acids having from 12'to 24 carbon atoms, such as lauric, palmitic, abietic (rosin), myristic, oleic, ricinoleic and stearic acids, and mixtures thereof, such as fatty acid mixtures derived from oils and fats such as coconut oil, palm oil, linseed oil, cottonseed oil, tallow, olive oil, soybean oil, whale and fish oils, oleostearine, lard, babassu oil, corn oil, castor oil, peanut oil, rosin, and greases.

It has been found that an amount of zinc compound to furnish an amount in the range within about 0.25 to 0.75 equivalent of zinc ion per gram equivalent weight of hydrosulfite is effective. It is desirable to employ the minimum amount of zinc compound which will overcome the odor, since excessive amounts of zinc ion may lead to formation of curdy precipitates when the finished soap is used in certain Waters. Ordinarily, 0.5 equivalent or less of zinc per gram equivalent weight of hydrosulfite is sufiicient and is preferred.

The following example illustrates application of the invention in the full-boiled process of making soap:

Two separate 1500 pound boils of a commercial toilet soap made by saponification with sodium hydroxide, using the full-boiled process, of fatty acid glycerides derived from tallow and coconut oil were treated with three pounds of sodium hydrosulfite (0.2% based upon the weight of the stock), approximately the proportion generally used in production boils. The hydrosulfite was added to both boils during the weak change, and after its addition the soap mass acquired a greyish cast and an objectionable odor characteristic of sulfur compounds. The mixture was allowed to settle and then the weak change lyes were drawn oil and the kettle boiled prior to finishing,

To one kettle (containing'2250 pounds of soap, calculated as 63% TFA) at 212 F. was added one pound (0.066% based upon the weight of the stock) of zinc sulfate crystals (ZnSOUII-IQO). After addition of the Zinc the soap boil lost its greyish cast and became white, and the objectionable odor disappeared. An additional pound of zinc sulfate crystals was added, but no further change was noted. The first addition of zinc sulfate amounted to 33.3% by weight of the hydrosulfite (0.26 gram equivalent of zinc ion per gram equivalent of hydrosulfite ion); after the second addition the amount of zinc sulfate was 71% by weight of the hydrosulfite (0.56 gram equivalent of zinc ion per gram equivalent of hydrosulfite ion). After addition of the zinc sulfate, a small quantity of caustic soda was added to adjust the alkalinity of the zinc boil to its original value. Both kettles were then finished in the regular manner.

The soap from each kettle was dried, mixed with the regular additives, including perfume, and finished into cakes. The perfume of the zinc sulfate-treated soap was considerably fresher and brighter than that of the untreated soap.

Although the invention has been described as applicable to soaps treated with ahydrosulfite, by any of the various methods of soap nianufacture, it is to be understood that it is applicable to any soap which contains disagreeable odors due to sulfur compounds. It may be used to eliminatehydrosulfite derived odors in soaps having all types of end uses, including toilet soaps, laundry soaps, and industrial soaps. It is especially useful with solid barsoaps, but is equally beneficial in connection with powdered, chip and liquid soaps.

It will be understood that many changes and of hydrosulfite-treated water-soluble fatty acid soaps which comprises adding thereto a watersoluble inorganic zinc compound in an amount to take up sulfur-containing odorand colorimparting residual hydrosulfite decomposition products by reaction therewith, and effecting the said reaction.

2. A process in accordance with claim 1 in which the zinc compound is zinc sulfate.

3. A process of preparing soap compositions which are substantially free of objectionable odors and have good color which comprises bleaching water-soluble fatty acid soap with a hydrosulfite, whereby the soap has a tendency to acquire an objectionable odor and a greyish color, and then treating the soap with a watersoluble inorganic zinc compound in an amount to substantially eliminate the odor and improve the color thereof.

4. A hydrosulfite-treated water-soluble fatty acid soap of which sulfur-containing color-and odor-imparting residual hydrosulfite decomposition products have been taken up by reaction with a water-soluble inorganic zinc compound in an amount to improve the color and odorof the soap.

FREDERICK J. SQUIRE. PETER D. STENGEL.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES .Modern Soap 81 Detergent Industry, Martin,

Crosby Lockwood Sons, London (1931) vol. 2 Sec.

6, page 17.

Oil, Paint and Drug Reporter, July 26, 1943 p. 

3. A PROCESS OF PREPARING SOAP COMPOSITIONS WHICH ARE SUBSTANTIALLY FREE OF OBJECTIONABLE ODORS AND HAVE GOOD COLOR WHICH COMPRISES BLEACHING WATER-SOLUBLE FATTY ACID SAOP WITH A HYDROSULFITE, WHEREBY THE SOAP HAS A TENDENCY TO ACQUIRE AN OBJECTIONABLE ODOR AND A GREYISH COLOR, AND THEN TREATING THE SOAP WITH A WATERSOLUBLE INORGANIC ZINC COMPOUND IN AN AMOUNT TO SUBSTANTIALLY ELIMINATE THE ODOR AND IMPROVE THE COLOR THEREOF. 